The haematopoietic system is a complex hierarchy of cells of different mature cell lineages. These include cells of the immune system that offer protection from pathogens, cells that carry oxygen through the body and cells involved in wound healing. All these mature cells are derived from a pool of haematopoietic stem cells (HSCs) that are capable of self-renewal and differentiation into any blood cell lineage. HSCs have the ability to replenish the entire haematopoietic system.
Haematopoietic cell transplantation (HCT) is a curative therapy for several inherited and acquired disorders. However, allogeneic HCT is limited by the poor availability of matched donors, the mortality associated with the allogeneic procedure which is mostly related to graft-versus-host disease (GvHD), and infectious complications provoked by the profound and long-lasting state of immune dysfunction.
Gene therapy approaches based on the transplantation of genetically modified autologous HSCs offer potentially improved safety and efficacy over allogeneic HCT. They are particularly relevant for patients lacking a matched donor.
The concept of stem cell gene therapy is based on the genetic modification of a relatively small number of stem cells. These persist long-term in the body by undergoing self-renewal, and generate large numbers of genetically “corrected” progeny. This ensures a continuous supply of corrected cells for the rest of the patient's lifetime. HSCs are particularly attractive targets for gene therapy since their genetic modification will be passed to all the blood cell lineages as they differentiate. Furthermore, HSCs can be easily and safely obtained, for example from bone marrow, mobilised peripheral blood and umbilical cord blood.
Efficient long-term gene modification of HSCs and their progeny requires a technology which permits stable integration of the corrective DNA into the genome, without affecting HSC function. Accordingly, the use of integrating recombinant viral systems such as γ-retroviruses, lentiviruses and spumaviruses has dominated this field (Chang, A. H. et al. (2007) Mol. Ther. 15: 445-56). Therapeutic benefits have already been achieved in γ-retrovirus-based clinical trials for Adenosine Deaminase Severe Combined Immunodeficiency (ADA-SCID; Aiuti, A. et al. (2009) N. Engl. J. Med. 360: 447-58), X-linked Severe Combined Immunodeficiency (SCID-X1; Hacein-Bey-Abina, S. et al. (2010) N. Engl. J. Med. 363: 355-64) and Wiskott-Aldrich syndrome (WAS; Bortug, K. et al. (2010) N. Engl. J. Med. 363: 1918-27). In addition, lentiviruses have been employed as delivery vehicles in the treatment of X-linked adrenoleukodystrophy (ALD; Cartier, N. et al. (2009) Science 326: 818-23), and very recently for metachromatic leukodystrophy (MLD; Biffi, A. et al. (2013) Science 341: 1233158) and WAS (Aiuti, A. et al. (2013) Science 341: 1233151).
Nevertheless, although lentiviruses are among the best available platforms for stem cell transduction, significant difficulties remain with the methods employed for the genetic modification of haematopoietic stem and progenitor cells.
In particular, the existing methods exhibit suboptimal target cell permissivity as high vector doses, prolonged transduction times and ex vivo culture are still required to reach clinically relevant transduction levels. This remains a significant hurdle for the field as it implies cumbersome, costly and not always sustainable large-scale vector productions and compromised cell quality due to prolonged ex vivo transduction protocols.
The prior art indicates that cyclosporin A (CsA) has a detrimental effect on the transduction of human CD34+ cells. For example, Santoni de Sio, F. R. et al. (2008) Stem Cells 26: 2142-52; Kahl, C. A. et al. (2008) Gene Therapy 15: 1079-89; and Uchida, N. et al. (2013) Exp. Hematol. 41: 779-88 e771 all teach that CsA decreases the transduction efficiency of HIV-1-derived vectors in human CD34+ cells.